This invention relates to dynamoelectric machines, and in particular, to a stator assembly and method of construction therefor. While the invention is described with particular reference to induction motors, those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
Conventionally, a dynamoelectric machine, of the induction motor type, for example, includes a stator assembly and a rotor assembly, each of which are constructed from a plurality of individual laminations formed from a suitable magnetic material. The lamination material commonly is slit to a predetermined width and fed through a punch press having a progressive die which punches or constructs the lamination silhouette in a series of steps. The rotor lamination is formed from the same lamination blank as the stator lamination. That is, in the progressive construction of the laminations, the stator lamination final design commonly has a yoke section having a central bore opening formed in it. A plurality of winding receiving slots extend radially outwardly from the central bore opening. The material removed from the material blank to form the central bore opening becomes the rotor lamination.
After the laminations are separated from the material blank from which they are formed, the individual laminations are segregated from one another and used to construct a stator core and a rotor core. Both the stator and rotor cores are formed from a plurality of the individual laminations, those laminations being secured to one another by any convenient method. In the case of the stator core, welding, cleating, adhesive bond or combination of these methods are commonly used expedients for core construction. Rotor cores for induction motors conventionally are of a squirrel cage design. The rotor laminations have a plurality of closed slots formed in them. Aluminum is cast in the rotor core slots to form the rotor conductor bars. The injection of the aluminum in the slots and the shorting of the rotor bars along the end faces of the rotor core hold the rotor core in the desired configuration.
The stator core has a suitable insulation positioned in the winding receiving slots, and the motor windings are placed in those slots. Thereafter, various finishing processes, not concerned with the present invention, are performed on the stator assembly. After construction of the stator and rotor assemblies, those assemblies are joined together to form a conventional induction motor. In the case of most induction motors, this is accomplished by supporting the rotor and its associated shaft along a pair of end shields, and placing the rotor within the bore opening of the stator assembly. It has been conventional to machine the outer diameter of the rotor assembly in order to permit its insertion within the bore opening and to provide the necessary air gap between the rotor and stator assemblies for proper motor operation. Machining is a relatively expensive and time consuming step in the motor construction process and a significant cost reduction is achieved if the machining operation can be eliminated.
Our invention eliminates the machining operation as a manufacturing step in motor construction. We accomplish this result by constructing a stator lamination having a yoke with a central bore opening formed in it. A plurality of slots extend radially outwardly from the bore opening. The area of the lamination between adjacent slots define a plurality of stator teeth. The lamination yoke lies in and defines a first plane area. Air gap between the stator and rotor in their final assembly is provided by bending the teeth of the individual stator laminations from the plane of the lamination yoke so that the final diameter of the central bore opening is larger than the opening provided when the teeth are essentially in the same plane as the yoke. Stator laminations often have varying depth winding receiving slots formed in them. As later described in detail, bending of certain ones of the teeth often also entails bending of the lamination yoke.
One of the objects of this invention is to provide a dynamoelectric machine which does not require a machining operation to provide air gap between the stator and rotor assemblies of the machine.
Another object is to provide a low cost dynamoelectric machine construction.
Yet another object is to provide a lamination for a dynamoelectric machine in which the teeth and portions of the yoke of the stator lamination are bent from a first plane initially containing both the teeth and the lamination yoke so that the bore opening diameter defined by the inboard surfaces of the teeth is larger than the bore opening diameter when the teeth and lamination yoke lie entirely in the first plane.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.